[LLVMbugs] [Bug 22803] New: shared_ptr's increment/decrement uses sequential consistency.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22803

            Bug ID: 22803
           Summary: shared_ptr's increment/decrement uses sequential
                    consistency.
           Product: libc++
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: martin.horenovsky at gmail.com
                CC: llvmbugs at cs.uiuc.edu, mclow.lists at gmail.com
    Classification: Unclassified

Current shared_ptr implementation uses sequential consistency for reference
counting, even though less strong atomics are good enough. This leads to
suboptimal performance for platforms other than x86 (x64).

Relaxed and acq/rel atomics (for increment and decrement respectively) should
be sufficient for thread safety. The reason it is currently implemented like
this was that Clang at the time didn't support full range of C++11 atomics and
noone ever got back to cleaning it up.

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